Method and device for controlling the piston movement of hydrostatic prime movers

ABSTRACT

A method of and apparatus for affecting the chronological course of movement of the working pistons of internal combustion operated prime movers, in which for purposes of converting the reciprocatory movement of the pistons into a rotary movement the transfer of power is effected through the intervention of hydraulic fluid in at least one hydraulic chamber, and according to which the quantity of hydraulic fluid in said hydraulic chamber is periodically changed whereupon following each change after a time period necessary for the working piston to carry out and/or two and/or four strokes, the quantity of hydraulic fluid prior to said change is restored in said hydraulic chamber.

United States Patent Kress 51 Jan. 18, 1972 [54] METHOD AND DEVICE FOR CONTROLLING THE PISTON MOVEMENT OF HYDROSTATIC PRIME MOVERS Inventor:

[72] Herwlg Kress,

Germany Filed: Jan. 26, 1970 Appl. No.: 5,675

[30] Foreign Application Priority Data Jan. 21, 1969 vs. cl. ..60/19, 60/545 R Int. Cl. ..F02b 41/00 Field 01 Search ..60/19, 26.11, 10.5, 54.5 R;

[56] References Cited UNITED STATES PATENTS 2,230,760 2/1941 Pescara.... ..eo/i9x' Klocken 5, 7981 Oberzell,

Germany... ..P 1903 851.8

2,391,972 1/1946 Huffordetal ..60/l.9UX 2,393,882 1/1946 Blair ..60/l.9

Primary Examiner-Edgar W. Geoghegan Attorney-Walter Becker [57] ABSTRACT A method of and apparatus for affecting the chronological 7 course of movement of the working pistons of internal combustion operated prime movers, in which for purposes of converting the reciprocatory movement of the pistons into a rotary movement the transfer of power is effected through the intervention of hydraulic fluid in at least one hydraulic chamber, and according to which the quantity of hydraulic fluid in said hydraulic chamber is periodically changed whereupon following each change after a time period necessary for the working piston to carry out and/0r two and/or four strokes, the quantity of hydraulic fluid prior to said change is restored in said hydraulic chamber.

11 Claims, 4 Drawing Figures PATENTED JAN18|972 3,635,014

SHEET 1 OF 2 IN VEN T 0/? {6/1/40 7704::

Pmmmmwmz 3.635014 SHEET 2 OF 2 FIG. 4

METHOD AND DEVICE FOR CONTROLLING THE PISTON MOVEMENT OF HYDROSTATIC PRIME MOVERS The present invention relates to a method of and device for controlling the piston movement of hydrostatic prime movers. The law of movement of pistons of ordinary internal com bustion engines or hot gas motors follows approximately a sine law. When, with hydrostatic power plants, the crankshaft is replaced by a circular eccentric, the piston movement follows even precisely a sine curve.

Actually it would be desirable to have the piston remain somewhat longer in the region of the lower dead center point in order thereby to improve the gas change and scavenging procedure. n the other hand, it would be desirable to shorten the time during which the piston is in the region of the upper dead center point in order thereby to reduce the wall losses caused by the high pressure and the high temperatures. Similarly, it would be desirable if, for instance with four-stroke cycle engines, each second upward stroke were shortened in order to prevent the piston from hitting the valves, or that, for better meeting certain conditions of operation, the stroke of the engine could be increased or reduced during operation. I

ln view of the considerable forceswhich have to be trans mitted with such engines and in view of the usually very high speeds at which the individualoperations or steps take place, it has heretofore been customary for converting the reciprocatory piston movement into a rotary movement to employ almost exclusively the simplest transmission which makes this conversion possible, namely a crank drive, or a modification thereof, namely an eccentric drive. Also with the so-called hydrostatic power machines, according to which the power transfer from the piston to the transmission for converting the reciprocatory movement into a rotary movement is eflected through the intervention of a hydraulic fluid enclosed in at least one chamber, it has been necessary for the above reasons to employ such transmissions.

It is, therefore, an object of the present invention to provide a method of and apparatus for overcoming the above-mentioned drawbacks.

It is another object of this invention to provide a method for effecting the timewise movement of the piston of prime movers according to which the power transfer from the piston to the transmission for converting the reciprocatory movement into a rotary movement is effected by means of a hydraulic fluid.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIGS. 1 and 2 diagrammatically illustrate two different embodiments according to the invention by means of which the method according to the invention may be practiced.

FIGS. 3 and 4 illustrate by way of graphs the course of movement of the working pistons of prime movers when applying the present invention.

According to the present invention it has been made possible to improve the course of movement of the piston of internal combustion engines with hydraulic power transmission to a considerable extent due to the fact that from the hydraulic chamber, which serves for the power transmission, there is withdrawn or added at least at one point a certain quantity of fluid and that the withdrawn or added quantity of hydraulic fluid is returned to or withdrawn from the hydraulic chamber after the time interval which is necessary for the piston to carry out one, two or four strokes. Thus, periodic operations are involved which are completed after one, two or four strokes while, depending on the requirements, also a plurality of such operations may take place parallel to and independently of each other.

In particular, the periodic withdrawal or addition of a certain quantity of hydraulic fluid may be effected by increasing or decreasing the volume of the hydraulic chamber in which the hydraulic fluid is enclosed and, more specifically, by making a part of the sidewalls of the hydraulic chamber movable.

According to a further development of the invention, the start of the withdrawal of hydraulic fluid from the hydraulic chamber or the increase in the volume of the hydraulic chamber is effected at a time at which the piston is precisely or approximately in its upper dead center position in which the heat is supplied to the gas enclosed by the piston in the cylinder, in other words, with internal combustion engines, in the upper dead center point in which the combustion occurs.

The withdrawal and return or the addition and rewithdrawal of the hydraulic fluid from the hydraulic chamber or the corresponding change in the volume of the chamber may be effected, according to the invention, precisely or approximately in conformity with the sine law because also in this instance, in view of the great forces involved, it is expedient to employ a crank drive or an eccentric or another equivalent driving system.

It is possible simultaneously to meet several of the abovementioned requirements by resorting to a plurality of the steps referred to above by means of which the change in the quantity of hydraulic fluid or the change in the volume of the hydraulic chamber can be made effective side by side. With four-stroke cycle engines, it is possible, in conformity with the invention, to bring about a superposition of the changes as to quantity and volume by effecting the withdrawal and return of hydraulic fluid from the hydraulic chamber with a frequency which equals twice the number of strokes of the piston per time unit, and'by superimposing upon the basic frequency an oscillation with such a frequency that, after two strokes of the piston, a maximum amplitude and a minimum amplitude of the withdrawing device alternate in a periodic sequence. This superposition is effected by a periodic adjustment of the device by means of which the magnitude of the change in the quantity of the hydraulicfluid is effected.

During the periodic withdrawal of hydraulic fluid and the subsequent return of the hydraulic fluid, generally a greater work than is actually used is conveyed to the driving system of the device employed for this purpose from the working process. Therefore it would be possible to forgo a separate drive for this device and merely to aim at a synchronization of the course of the withdrawal and addition of hydraulic fluid with the stroke movement of the working piston. This, however, would mean giving up a part of the power produced in the working process. This can be avoided according to the invention by seeing to it that the driving system of the device which brings about the periodic change in the quantity of hydraulic fluid is driven directly by or drives the main drive shaft of the prime mover or through the intervention of a transmission at the ratio l:2 or 2:1.

Similarly, according to the invention improved operation is provided when the drive of the structural elements bring about the periodic adjustment of the device in conformity with the speed of the camshaft of a four-stroke cycle engine; such periodic adjustment in turn brings about the change in the quantity of the hydraulic fluid; under forgoing circumstances, it is advantageous with the invention when the drive of the structural elements is effected by the camshaft itself or is effected by the main drive shaft of the internal combustion engine through the intervention of a stepdown transmission.

With automatically guided oil pistons of hydrostatic power machines, it is a known fact that both sides of the oil piston are in communication with the hydraulic fluid, while the oil piston itself is positively connected to the working piston. In this instance, in conformity with the present invention, a quantity of hydraulic fluid which equals the quantity of hydraulic fluid withdrawn from the first hydraulic chamber must at the ratio of the power-effective surfaces of both sides of the oil piston be adapted to be conveyed to the second hydraulic chamber and vice versa.

Furthermore, it may be desirable to control these operations in conformity with time or in any other suitable way. To this end, the invention provides that at least one of the devices for changing the quantity of the hydraulic fluid can, with respect to the start of the withdrawing operation or with respect to the quantity withdrawn from or added to the hydraulic chamber, be varied manually or in conformity with one or more control factors either temporarily or permanently.

According to the present invention it may be advantageous, in some instances, to arrange the device for periodically changing the quantity of the hydraulic fluid entirely or partially in the interior of the main drive shaft.

Referring now to the drawings in detail, according to the embodiment shown in FIG. 1, a piston 2 is reciprocable in a cylinder 2. The cylinder head 1a closes the upper portion of the working chamber lb of the prime mover. The piston 2 is through a piston rod 3 connected to the oil piston 4 which is movable in the oil cylinder 5. Below the oil piston 4 there is provided a hydraulic chamber 6 which in addition to the oil piston 4 is confined by the hydraulic chamber 7, the eccentric 8 and the slide 10. The eccentric 8 rotates about the central axis of the main drive shaft 9 connected thereto which shaft 9 is offset by the length E with regard to the central axis of the eccentric 8. The slides 10 are mounted in sleeves 10a and are pressed against the surface of the eccentric by the force P. Since the oil acting as hydraulic fluid is compressible only to a minor extent, the position of the oil piston 4 and thereby of the working piston 2 is a function of the angular position of the eccentric 8. lnasmuch as with this example an eccentric 8 with circular outer contour is employed, the movement of the piston follows a simple sine law.

A deviation from this course may be obtained by withdrawing from the hydraulic chamber 6 during one or a plurality of working steps a certain quantity of hydraulic fluid and by returning this quantity of fluid after one, two or four strokes to the hydraulic chamber. According to the example of FIG. 1 the same effect is realized during the above-mentioned cycle by first increasing the volume of hydraulic chamber 6 in which the hydraulic fluid is enclosed and then again reducing the volume of said hydraulic chamber 6. By providing a control cylinder 11 and a control piston 12 reciprocable therein, a portion of the otherwise stationary sidewalls of the hydraulic chamber 7 has become movable whereby an increase in the volume of the chamber can be obtained which affects the position of the oil piston 4. To the extent to which the control piston 12 moves upward or outwardly, there is obtained a downward movement of the oil piston 4 and of the working piston 2 connected thereto, assuming that in the meantime the eccentric 8 has not been rotated. Actually, both movements are superimposed upon each other.

According to the embodiment of FIG. 1, the control piston 12 is through the piston bolt 13 in connection with the connecting rod 14 which in its turn is by means of the crankpin 15 connected to the crank web 16. The axis of rotation of the crankshaft is designated with the reference numeral 17.

The effective length e of the crank web 16 determines the stroke length of the control piston 12 and together with the diameter of the control piston 12 determines the increase in the volume of the hydraulic chamber during a working cycle.

According to the embodiment of FIG. 1, in order to explain the functions, very simple structural elements have been selected for the eccentric 8 and its control slide 10 as well as for the control piston 12 with the succeeding crank drive. In practice, however, different designs are selected in which, for instance, the individual structural elements are relieved from pressure or the linear seal of the present system, slide 10 and eccentric 8, are replaced by a surface seal. Similarly, instead of the crank drive for the control piston there may be employed, for instance, a rotary piston system, or the like, or a hydrostatic drive system may be employed.

FIG. 3 illustrates how by means of the arrangement shown in HO. 1 it is possible to control the course of movement of an internal combustion engine of the two-stroke cycle type. The curve 0 indicated in dashlines indicates the course of the piston movement plotted over the time when, with the arrangement of FIG. 1, only the eccentric 8 rotates while the control piston 12 is held stationary. In this instance a pure sine-shaped stroke movement is involved as it is present with very close approximation also with ordinary crank drives. lf now the control piston 12 is put into motion in such a way that its crankshaft has the speed 2n while the main drive shaft moves at the speed In, and if furthermore the increase in the volume of the hydraulic chamber 6, brought about by the movement of the control piston 12, starts when the piston 2 occupies its upper dead center point, the withdrawal curve represented by the curve c is obtained according to which the quantity of hydraulic fluid withdrawn from the hydraulic chamber 6 is indicated by shading. The superposition of the curves a and c results in the course b of the stroke movement of the piston 2.

In the present instance, according to FIG. 3, it is assumed that the displacement volume of the cylinder 1 is V,,=l 00 percent, whereas the displacement volume of the control cylinder 11 amounts to V =20 percent. In this instance the withdrawal of hydraulic oil in the upper and lower dead center point of the working cylinder equals zero, while the withdrawal maximum of 20 percent of V takes place with a sine-shaped course of the curve 0 with each crank web past the upper and lower dead center point. Thus, while the time required for the heat transfer in the vicinity of the upper dead center point, which time has been designated with a, with the course of movement according to the noninfluenced curve a, is in view of the withdrawal of hydraulic oil reduced to the considerably shorter time 01,, and the time available for the gas change in the lower dead center point increases to an even greater extent, this time being designated with a for the curve a and with 0: for the curve b. Thus, in this instance, in confonnity with the curve b at the same speed n of the main drive shaft 9, the compression stroke as well as the expansion stroke take less time than heretofore, whereas at the same time the time available for the gas change procedure and for the total cooling off the piston has increased. Thus, under otherwise identical conditions it is possible to load the combustion chamber to a considerably greater extent and also to increase the speed because the time available for the gas change is relatively longer.

In the above example the start of the upward movement of the control piston 12 coincides with the time at which the piston 2 occupies its upper or lower dead center point. However, it may also be expedient to have this movement start short prior to or after this time. In the last-mentioned instance, a somewhat different and in special instances more favorable course will be obtained for the resultant curve, while, among other, there also exists the possibility somewhat to increase the stroke of the working piston.

Inasmuch as the control piston 12 generally receives a larger amount of work than it consumes, it is sometimes expedient to connect the control piston 12 through a transmission to the main drive shaft 9 in order to avoid work losses. In other instances, especially when the control stroke is very short, it will suffice to synchronize the movement of the control piston 12 at twice the rhythm of the movement of the working piston or the main drive shaft.

The movement of the control piston 12 may, provided that it occurs at the rhythm of the speed of the working piston, i.e., without the interposition of a stepdown or step-up transmission between the main drive shaft 9 and the crankshaft 17 of the control transmission 11-17, also be employed for increasing the volume of the working cylinder.

This provision may be used, for instance, when within the range of a lower speed, an increased stroke volume is desired in order to improve the course of the torque in conformity with the speed without the necessity of having to increase the medium piston speed within the range of a very high speed, which frequency represents a limiting factor. lt is possible to control this stroke movement in conformity with the speed of rotation, for instance by providing means with which the control transmission 11-17 change the length e of the crank web in conformity with the speed or, if, in conformity with the invention, a mutual phase displacement is effected between the respective main drive shaft 9 rotating at the speed it and the crankshaft 17 of the control transmission, which main drive shaft and crankshaft will, after the said phase displacement has been effected, again operate in synchronism. In order to obtain the desired pressure, it is necessary once additionally to feed a certain quantity of hydraulic fluid into the hydraulic chamber 6 if the control piston 12, in case the length of the crankshaft e has become zero, is spaced from the hydraulic chamber 7 by the distance e/2. An equivalent step could consist in displacing the axis 17 of the crankshaft of the control drive by the length e/ 2 in the direction toward the wall of the hydraulic fluid chamber, or generally by displacing the axis 17 of the crankshaft with the change in the length 2 of the crank web 16 to such an extent in the direction of the hydraulic fluid chamber 7 that the minimum withdrawal quantity will be obtained at any rate during one cycle.

If with four-stroke cycle engines, in view of the valve movement in the upper dead center point of the piston 2 where the gas change occurs, it should be desirable to have the upward stroke of the piston 2 somewhat shorter than the compression stroke, this can be realized by withdrawing hydraulic fluid from the hydraulic chamber 6 at a frequency equaling n/2, while also in this instance the start of the withdrawal is effected at the upper dead center point where the combustion takes place. Instead of providing a separate control device for this purpose, it is also possible to decrease the length e of the crank web 16 in the above-mentioned rhythm, i.e., with a speed which is proportional to the speed of rotation n/2, if desired up to the value zero or also to a negative value.

FIG. 4 illustrates by way of a graph the effect of such a measure of the course of the withdrawal curve g in dependency of the time when after 360 crank rotation the length e of the crank web 16 has become zero;

According to FIG. 4, the curve a again represents the noninfluenced sine-shaped course of movement of the working piston 2, whereas the curve d represents the course of movement of the working piston 2 as it results from the superposition of the curves a and g. The curve f in this graph furthermore indicates how the length e of the crank web 16 varies in conformity with time. The change of the value e may expediently be effected directed through the intervention of a drive system which is coupled to the camshaft of the fourstroke cycle engine, or it may also be effected through a stepdown transmission 2:1 from the main drive shaft 9.

A further embodiment of the invention is shown in FIG. 2 according to which the piston 2 is through a piston rod 3 connected to a double-acting oil piston 4a. In this instance, two hydraulic chambers 60 and 6b are provided which are respectively formed by the space confined by the oil piston 4a, the oil cylinder 5a, the sealing sleeves 5b, the connecting lines 18 and the space confined by the hydraulic fluid chamber 7, the eccentric 8 and the sealing slides 110. This arrangement may be necessary in order to assure with a hydrostatic machine that also during the upward movement of the piston 2, when the speed of movement decreases in the second half of the stroke, a reliable contact is always obtained between the bottom side of the oil piston 4a and the hydraulic fluid enclosed in the hydraulic fluid chamber 611.

Therefore, if a certain quantity of hydraulic fluid is withdrawn from the lower hydraulic chamber 6a to thereby influence the course of movement of the working piston in the above-referred-to way, it is necessary, in case both piston sides have the same surface, to convey the same quantity of hydraulic fluid into the upper hydraulic chamber 6b. This is made possible by the device illustrated on the left-hand side of FIG. 2. The designations are the same as in FIG. 1. Merely the double-acting control piston has been designated with the reference numeral 12a, the doubleacting control cylinder has been designated with the reference numeral 11a, the pertaining sealing sleeves have been designated with the reference numerals lib, and the conduits through which the hydraulic fluid is conveyed from the hydraulic chambers 6a and 6b have been designated with the reference numerals I9.

If the effective piston surfaces of the double-acting oil piston are not of equal size, it is necessary to effect the withdrawal and addition of hydraulic fluid in conformity with the effective surface conditions, for instance, by designing the control piston 12a as stepped piston. Similar remarks apply to the design of the eccentric system 7-10 of FIG. 2.

Also in this instance, the illustration of FIG. 2 is merely meant to show the principle of the arrangement according to the invention while it does not exhaust other numerous possibilities to realize the principle according to the invention.

A particularly favorable possibility of installing the device according to the invention for withdrawing and returning hydraulic fluid within the frame work of a machine concept consists in employing for this purpose the space in the interior of the eccentric for which purpose the eccentric 8 must be made hollow. In this way, very short lengths for the connecting lines 19 will result which is essential for keeping the losses low, and furthermore the wall of the eccentric 8 itself may form the housing for the control cylinders 5, 5a which are mounted in the eccentric. Also, control piston means for periodically changing the quantity of hydraulic fluid in the hydraulic chamber means can be at least partially located within the main shaft 9.

It is, of course, to be understood that the present invention is, by no means, limited to the particular constructions shown in the drawings but also comprises any modifications within the scope of the appended claims.

What I claim is:

1. A method of variably affecting the modification of the chronological course of movement of the working pistons of internal combustion operated prime movers, in which for purposes of converting the reciprocatory movement of the pistons into a rotary movement the transfer of power is effected through the interposition of hydraulic fluid in at least one hydraulic chamber, which includes the steps of: periodically changing the quantity of hydraulic fluid in said hydraulic chamber, and after a time period necessary for the working piston to selectively carry out at least one stroke again restoring said quantity of hydraulic fluid which existed prior to said changing.

2. A method according to claim 1, in which said periodical changing in the quantity of hydraulic fluid in said hydraulic chamber is effected particularly by changing the volume of said hydraulic chamber.

3. A method according to claim 1, in which the periodical changing in the quantity of hydraulic fluid in said hydraulic chamber in initiated at the time at which said working piston is at least approximately in its upper dead center position where the heat supply to gas entrapped by said working piston is effected.

4. A method of affecting the chronological course of movement of the working pistons of internal combustion operated prime movers, in which for purposes of converting the reciprocatory movement of the pistons into a rotary movement the transfer of power is effected through the interposition of hydraulic fluid in at least one hydraulic chamber, which includes the steps of: periodically changing the quantity of hydraulic fluid in said hydraulic chamber, and after a time period necessary for the working piston to selectively carry out at least one stroke restoring said quantity of hydraulic fluid prior to said changing, the periodical changing in the quantity of hydraulic fluid in said hydraulic chamber being effected at least approximately in conformity with a sine law.

5. A method of affecting the chronological course of movement of the working pistons of internal combustion operated prime movers, in which for purposes of converting the reciprocatory movement of the pistons into a rotary movement the transfer of power is effected through the interposition of hydraulic fluid in at least one hydraulic chamber, which includes the steps of: periodically changing the quantity of hydraulic fluid in said hydraulic chamber, and after a time period necessary for the working piston to selectively carry out at least one stroke restoring said quantity of hydraulic fluid prior to said changing, said periodical changing in the quantity of hydraulic fluid in said hydraulic chamber being effected at a frequency equaling twice the number of strokes of the working piston per time unit, said frequency which forms the basic frequency having superimposed an oscillation with such a frequency that after each two strokes of the working piston a maximum amplitude and a minimum amplitude in the withdrawal of the hydraulic fluid from said hydraulic chamber periodically alternate.

6. An apparatus for affecting the chronological course of movement of working pistons of internal combustion operated prime movers, which includes: hydraulic chamber means, oil piston means operatively connected to said prime mover and operable by said prime mover for reciprocation in said hydraulic chamber means, rotatable eccentric means extending into said hydraulic chamber means and operatively connected to the main shaft of said prime mover, slide means in substantial sealing engagement with said eccentric means and together with said eccentric means forming a wall portion of said hydraulic chamber means, control piston means reciprocable in said hydraulic chamber means for periodically changing the quantity of hydraulic fluid in said hydraulic chamber means, and driving means operable by the main shaft of said prime mover for actuating said control piston means.

7. An apparatus according to claim 6, which includes camshaft means operable by the main shaft of a prime mover and drivingly connected to said control piston means.

8. An apparatus according to claim 7, which includes a stepdown transmission preceding said camshaft means and drivingly connected thereto.

9. An apparatus according to claim 6, in which said hydraulic chamber means includes two hydraulic chambers, and in which a wall portion of each of said chambers is respectively formed by one of two opposite sides of said oil piston means, said apparatus also including means communicating with said hydraulic chambers for conveying to one of said chambers the same quantity of hydraulic fluid which is displaced from the other one of said chambers and vice versa.

10. An apparatus according to claim 6, in which said control piston means has associated therewith means operable selectively to vary the operation of said control piston means.

11. An apparatus according to claim 6, in which said control piston means for periodically changing the quantity of hydraulic fluid in said hydraulic chamber means is at least partially located operatively within range of said main shaft. 

1. A method of variably affecting the modification of the chronological course of movement of the working pistons of internal combustion operated prime movers, in which for purposes of converting the reciprocatory movement of the pistons into a rotary movement the transfer of power is effected through the interposition of hydraulic fluid in at least one hydraulic chamber, which includes the steps of: periodically changing the quantity of hydraulic fluid in said hydraulic chamber, and after a time period necessary for the working piston to selectively carry out at least one stroke again restoring said quantity of hydraulic fluid which existed prior to said changing.
 2. A method according to claim 1, in which said periodical changing in the quantity of hydraulic fluid in said hydraulic chamber is effected particularly by changing the volume of said hydraulic chamber.
 3. A method according to claim 1, in which the periodical changing in the quantity of hydraulic fluid in said hydraulic chamber in initiated at the time at which said working piston is at least approximately in its upper dead center position where the heat supply to gas entrapped by said working piston is effected.
 4. A method of affecting the chronological course of movement of the working pistons of internal combustion operated prime movers, in which for purposes of converting the reciprocatory movement of the pistons into a rotary movement the transfer of power is effected through the interposition of hydraulic fluid in at least one hydraulic chamber, which includes the steps of: periodically changing the quantity of hydraulic fluid in said hydraulic chamber, and after a time period necessary for the working piston to selectively carry out at least one stroke restoring said quantity of hydraulic fluid prior to said changing, the periodical changing in the quantity of hydraulic fluid in said hydraulic chamber being effected at least approximately in conformity with a sine law.
 5. A method of affecting the chronological course of movement of the working pistons of internal combustion operated prime movers, in which for purposes of converting the reciprocatory movement of the pistons into a rotary movement the transfer of power is effected through the interposition of hydraulic fluid in at least one hydraulic chamber, which includes the steps of: periodically changing the quantity of hydraulic fluid in said hydraulic chamber, and after a time period necessary for the working piston to selectively carry out at least one stroke restoring said quantity of hydraulic fluid prior to said changing, said periodical changing in the quantity of hydraulic fluid in said hydraulic chamber being effected at a frequency equaling twice the number of strokes of the working piston per time unit, said frequency which forms the basic frequency having superimposed an oscillation with such a frequency that after each two strokes of the working piston a maximum amplitude and a minimum amplitude in the withdrawal of the hydraulic fluid from said hydraulic chamber periodically alternate.
 6. An apparatus for affecting the chronological course of movement of working pistons of internal combustion operated prime movers, which includes: hydraulic chamber means, oil piston means operatively connected to said prime mover and operable by said prime mover for reciprocation in said hydraulic chamber means, rotatable eccentric means extending into said hydraulic chamber means and operatively connected to the main shaft of said prime mover, sliDe means in substantial sealing engagement with said eccentric means and together with said eccentric means forming a wall portion of said hydraulic chamber means, control piston means reciprocable in said hydraulic chamber means for periodically changing the quantity of hydraulic fluid in said hydraulic chamber means, and driving means operable by the main shaft of said prime mover for actuating said control piston means.
 7. An apparatus according to claim 6, which includes camshaft means operable by the main shaft of a prime mover and drivingly connected to said control piston means.
 8. An apparatus according to claim 7, which includes a stepdown transmission preceding said camshaft means and drivingly connected thereto.
 9. An apparatus according to claim 6, in which said hydraulic chamber means includes two hydraulic chambers, and in which a wall portion of each of said chambers is respectively formed by one of two opposite sides of said oil piston means, said apparatus also including means communicating with said hydraulic chambers for conveying to one of said chambers the same quantity of hydraulic fluid which is displaced from the other one of said chambers and vice versa.
 10. An apparatus according to claim 6, in which said control piston means has associated therewith means operable selectively to vary the operation of said control piston means.
 11. An apparatus according to claim 6, in which said control piston means for periodically changing the quantity of hydraulic fluid in said hydraulic chamber means is at least partially located operatively within range of said main shaft. 